In certain factory and office building, circuits for operating heating and air conditioning apparatus for various parts of the building are controlled by conventional individual thermostats which have a limited range of adjustment. Thus, the lowest adjustment for the control for heating apparatus may be 50.degree. F. in work or office space. Also, while apartments, motels and like buildings generally are arranged permiting localized adjustments of the controlled temperatures in the individual units, the occupants of the units may be unwilling to adjust the controls to lower the heating temperatures and raise the cooling temperatures such as is now considered necessary for energy conservation, particularly during all or some of the night hours. In some of these locations, such as work space in a factory building, it may be desirable and perfectly safe when the space is not being used to maintain certain heating apparatus off for so long as the inside temperature exceeds 40.degree. F. In apartments and like buildings, overriding the occupants' adjustments of controls for heating and air conditioning apparatus from remote locations may be necessary to insure that an appropriate temperature limit is imposed.
While the problem has been generally recognized, previous solutions generally have involved the high cost of providing separate additional control wiring and other equipment and of installing that equipment. Thus, some prior systems have employed low voltage cables, thereby eliminating the need to install protective conduits or large gauge wiring. Other prior systems used multiplexing to combine all their signals onto a few coaxial cables. But the need to use additional wiring and for sophisticated multiplexing equipment was not eliminated thereby.
A known control system, such as illustrated in U.S. Pat. No. 4,021,615 to James et al overcomes the need for providing additional building wiring by transmitting control pulse bursts over exitsing telephone lines. The system has disadvantages inter alia that (1) the transmitting control circuitry must be tapped into each phone line at the branch exchange; (2) the system receivers must be tapped into the phone lines at each remote location; and remote receivers can only be located in areas of the building served by phone lines, typically less than all of the building.
Accordingly, it is an object of the present invention to provide a wireless control system for electrical apparatus, which system utilizes the same wiring used to connect the apparatus to the electric supply.
It is another object of the present invention to provide a temperature control system wherein control signals are conveyed to temperature controlling apparatus over electric power line wiring for the enclosure having its temperature controlled.
It is still another object of the invention to provide a temperature control system including a master transmitter for applying control signals determined by temperature and time at a master location to power lines for transmission thereby to receiver's at the location of controlled apparatus along the power lines.
These and other objects and advantages of the present invention will be apparent from the claims and from the following detailed description when read in conjunction with the appended drawings.